This invention relates to an X-ray image sensor used for industrial and remedial purposes.
A known X-ray image sensor utilizing a solid state imaging device uses a phosphor having a light emission range near 500 nm for a phosphor layer.
In the conventional X-ray image sensor utilizing the phosphor having its light emission range near 500 nm, the thickness of the phosphor layer must be great for sufficiently absorbing the X-rays in order to prevent coloring damage of the fiber optic plate. Since ordinary transmission inspection apparatuses use X-rays of from 10 to 100 KeV, this thickness is at least one millimeter. At this time the image which changes from the X-rays to visible rays diffuses in the phosphor layer and there occurs the problem that resolution drops below 51 p/mm.
To form the phosphor layer in a thin film and to improve resolution, a system has been proposed which adds cerium oxide to the fiber plate so as to prevent coloration but this system is not free from the problem that the production cost becomes high because cerium oxide must be specifically added.